3 files changed, 21 insertions, 7 deletions
diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index c8b16c115e..dee026e3a0 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -103,7 +103,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
   DEFAULT <replaceable>default_expr</replaceable> |
   GENERATED ALWAYS AS ( <replaceable>generation_expr</replaceable> ) STORED |
   GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ] |
-  UNIQUE <replaceable class="parameter">index_parameters</replaceable> |
+  UNIQUE [ NULLS [ NOT ] DISTINCT ] <replaceable class="parameter">index_parameters</replaceable> |
   PRIMARY KEY <replaceable class="parameter">index_parameters</replaceable> |
   REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
     [ ON DELETE <replaceable class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ] }
@@ -113,7 +113,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
 
 [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
 { CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
-  UNIQUE ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
+  UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
   PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
   EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ] |
   FOREIGN KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ] ) ]
diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index 89a4d746f6..91eaaabc90 100644
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -24,6 +24,7 @@ PostgreSQL documentation
 CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class="parameter">name</replaceable> ] ON [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ USING <replaceable class="parameter">method</replaceable> ]
     ( { <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable class="parameter">opclass</replaceable> [ ( <replaceable class="parameter">opclass_parameter</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
     [ INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ]
+    [ NULLS [ NOT ] DISTINCT ]
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
     [ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]
     [ WHERE <replaceable class="parameter">predicate</replaceable> ]
@@ -335,6 +336,18 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
      </varlistentry>
 
      <varlistentry>
+      <term><literal>NULLS DISTINCT</literal></term>
+      <term><literal>NULLS NOT DISTINCT</literal></term>
+      <listitem>
+       <para>
+        Specifies whether for a unique index, null values should be considered
+        distinct (not equal).  The default is that they are distinct, so that
+        a unique index could contain multiple null values in a column.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
       <term><replaceable class="parameter">storage_parameter</replaceable></term>
       <listitem>
        <para>
diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index b97bb9ded1..7e4ef312c0 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -67,7 +67,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
   DEFAULT <replaceable>default_expr</replaceable> |
   GENERATED ALWAYS AS ( <replaceable>generation_expr</replaceable> ) STORED |
   GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ] |
-  UNIQUE <replaceable class="parameter">index_parameters</replaceable> |
+  UNIQUE [ NULLS [ NOT ] DISTINCT ] <replaceable class="parameter">index_parameters</replaceable> |
   PRIMARY KEY <replaceable class="parameter">index_parameters</replaceable> |
   REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
     [ ON DELETE <replaceable class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ] }
@@ -77,7 +77,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
 
 [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
 { CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
-  UNIQUE ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
+  UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
   PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
   EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ] |
   FOREIGN KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ] ) ]
@@ -917,8 +917,8 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
    </varlistentry>
 
    <varlistentry>
-    <term><literal>UNIQUE</literal> (column constraint)</term>
-    <term><literal>UNIQUE ( <replaceable class="parameter">column_name</replaceable> [, ... ] )</literal>
+    <term><literal>UNIQUE [ NULLS [ NOT ] DISTINCT ]</literal> (column constraint)</term>
+    <term><literal>UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] )</literal>
     <optional> <literal>INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ...])</literal> </optional> (table constraint)</term>
 
     <listitem>
@@ -934,7 +934,8 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
 
      <para>
       For the purpose of a unique constraint, null values are not
-      considered equal.
+      considered equal, unless <literal>NULLS NOT DISTINCT</literal> is
+      specified.
      </para>
 
      <para>